Dose transfer standard detector for a lithography tool

ABSTRACT

A dose transfer standard detector measures radiation intensity and dose in a lithography tool. The lithography tool may be an Extreme Ultraviolet lithography (EUVL) tool. The dose transfer standard detector may transmit intensity and dose data to a computer, which analyzes the data. Based on the analyzed data, the lithography tool may be calibrated.

BACKGROUND

A microchip manufacturing process may deposit various material layers ona wafer and form a photosensitive film or photoresist on one or moredeposited layers. A lithography tool may transmit light throughtransmissive optics or reflect light from reflective optics to a reticleor patterned mask. Light from the reticle transfers a patterned imageonto the photoresist. Portions of the photoresist which are exposed tolight may be removed. Portions of the wafer which are not protected bythe remaining photoresist may be etched to form transistor features.

The semiconductor industry may continue to reduce the size of transistorfeatures to increase transistor density and improve transistorperformance. This reduction in transistor feature size has driven areduction in the wavelength of light used in lithography tools to definesmaller transistor features on a photoresist.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example of a lithography tool, such as an ExtremeUltraviolet lithography (EUVL) tool.

FIG. 2 illustrates a dose transfer standard detector structure which maybe used in the lithography tool of FIG. 1.

FIG. 3 illustrates the dose transfer standard detector structure of FIG.2, two lithography tools and a computer.

FIG. 4 shows a flow chart of using the dose transfer standard detectorof FIG. 2.

FIG. 5 illustrates an alternative embodiment of the dose transferstandard detector structure of FIG. 2.

DETAILED DESCRIPTION

Extreme Ultraviolet lithography (EUVL) may use a radiation wavelength ofapproximately 11-15 nanometers (nm). An EUV lithography tool may print apattern on a photoresist with dimensions which are smaller thandimensions achieved by other lithography tools. An EUV lithography toolmay also be called a “lithographic exposure system,” an “EUV scanner” oran “EUV stepper.”

FIG. 1 illustrates an example of a lithography tool 100, such as anExtreme Ultraviolet lithography (EUVL) tool. The lithography tool 100may include a laser 102, an electric discharge or laser produced plasmasource 104, condenser optics 106, a reflective reticle 107 with apattern, and reflective reduction optics 108. The reticle 107 may beused to form a patterned image on an object 110, such as a silicon waferwith a photoresist layer.

“Intensity” (milliWatts/cm²) refers to an amount of radiation incidentupon the object 110 in the lithography tool 100. “Dose”(milliJoules/cm²) refers to an amount of energy absorbed by the object110 in the lithography tool 100. A user may set radiation intensity anddose for a lithography tool according to a standard reference. Thestandard reference may be based on values provided by the NationalInstitute of Standards & Technology (NIST). The intensity and dose mayvary slightly from lithography tool to lithography tool even though thelithography tools have the same settings. Intensity and dose may alsochange (“drift”) after a lithography tool is shipped or after repeatedused.

It may be desirable to measure and calibrate the intensity and dose of alithography tool. It may be desirable to compare and match the intensityand dose of two or more lithography tools.

It may be difficult to access a wafer stage of a conventionallithography tool to install hardware to measure radiation intensity anddose. A lithography tool may have a vacuum or non-vacuum wafer stage.For a lithography tool with a non-vacuum wafer stage, a person may enterthe lithography tool and manually connect radiation detection hardwareto the wafer stage.

For a lithography tool with a wafer stage in a vacuum, such as an EUVlithography tool, a person may have to break the vacuum to installradiation detection hardware to the wafer stage. Alternatively, a robotmay be inserted in an interlock chamber connected to the vacuum toinsert radiation detection hardware to the wafer stage.

The present application relates to a dose transfer (or dose transport)standard detector and techniques of using the same. The detector mayaddress the challenges of moving a dose detector between two or morelithography tools. The detector may be easily loaded and unloaded on awafer stage of a lithography tool, such as an extreme ultravioletlithography (EUVL) tool. The detector may accurately measure theintensity and/or dose of one or more vacuum or non-vacuum lithographytools. The size, shape and components of the detector may automateloading of the detector, alignment of the detector, and collection ofintensity and dose data. A computer may compare data from the detectorwith a reference value.

FIG. 2 illustrates a dose transfer standard detector structure 200,which may be used in the lithography tool 100 of FIG. 1. Lithographytools may handle the dose transfer standard detector structure 200 asany other wafer. The detector structure 200 may include a wafer 201fabricated with an array of detectors 206, one or more amplifiers 202, aprocessor 203, a wireless transmitter 204, a power source 207 andalignment marks 205.

The processor 203 in FIG. 2 may be a digital signal processor availablefrom Intel Corporation. The power source 207 in FIG. 2 may becapacitive, electrolytic, photovoltaic or some other type of powersource. The alignment marks 205 allow the wafer 201 to be aligned on awafer stage of the lithography tool 100.

The detectors 206 in FIG. 2 may be adapted to detect radiation intensity(milliWatts/cm²) incident upon the wafer 201 and/or dose(milliJoules/cm²) when the wafer 201 is in the lithography tool 100. Thedetectors 206 may include photodiodes. For example, the detectors 206may include a silicon photodiode. The detectors 206 may detect extremeultraviolet (EUV) radiation and other types of radiation. An array ofdetectors 206 may be used since intensity and/or dose may vary (e.g.,0.5%) over multiple detectors. An average intensity and/or dose overmultiple detectors may be calculated in an embodiment.

The temperature of the wafer stage inside the lithography tool 100 maybe carefully controlled such that the detectors 206, amplifiers 202,processor 203, wireless transmitter 204, and power source 207 on thewafer 201 do not experience a substantial temperature change. The arrayof detectors 206 may be the only components on the wafer 201 exposed toradiation in the lithography tool 100 in an embodiment.

FIG. 3 illustrates the dose transfer standard detector structure 200 ofFIG. 2 being used with first and second lithography tools 302A, 302B anda computer 304. The lithography tools 302A, 302B may be similar to thelithography tool 100 of FIG. 1.

FIG. 4 shows a flow chart for using the dose transfer standard detectorstructure 200 of FIG. 2. The detector structure 200 may be loaded andaligned on a wafer stage of the first lithography tool 302A (FIG. 3) at400 in FIG. 4. The first lithography tool 302A may be activated toproduce radiation on the detectors 206 of the wafer 201. The array ofdetectors 206 may detect a radiation dose and/or intensity and produceone or more signals. One or more amplifiers 202 may amplify signals fromthe detectors 206. The processor 203 may process or convert amplifiedsignals from the amplifiers 202 to a form which may be transmitted bythe transmitter 204. The transmitter 204 may wirelessly transmit signalscorresponding to dose and/or intensity data to the computer 304 (FIG. 3)while the detector structure 200 is inside the first lithography tool302A.

In alternative embodiment, the detector structure 200 stores dose and/orintensity data in an optional memory 210. When the detector structure200 comes out of the first lithography tool 302A, the detector structure200 may transfer dose and/or intensity data in the memory 210 to thecomputer 304 wirelessly or via a physical output connector.

The computer 304 may analyze the dose and/or intensity data from thedetector structure 200 at 402. The computer 304 may collect and analyzedata remotely. The computer 304, or a user using data from the computer302, may compare the dose and/or intensity data from the detectorstructure 200 to a reference, such as a user-defined setting on thefirst lithography tool 302A. The computer 304 or a user may determine ifthe detected dose and/or intensity substantially matches the reference.

If the computer 304, or a user using the computer 302, determines thatthe detected dose and/or intensity does not substantially match thereference, the computer 304 or user may adjust settings or calibrationsof the first lithography tool 302A at 404. For example, the firstlithography tool 302A may be set to produce a desired dose of 10milliJoules/cm² (e.g., by calibrating the laser 102 in FIG. 1). But thedetector structure 200 loaded in the first lithography tool 302A detectsan actual dose of 9.5 milliJoules/cm². The computer 304, or a user usingthe computer 302, may adjust the first lithography tool 302A to 10.5milliJoules/cm². The first lithography tool 302A may then produce anactual dose of 10 milliJoules/cm².

The actions described above at 400 through 404 may be repeated toachieve a desired level of accuracy for dose and/or intensity of thefirst lithography tool 302A.

If the computer 304, or a user using the computer 302, determines thatthe detected dose and/or intensity does substantially match thereference, the dose transfer standard detector structure 200 may beloaded and aligned on a wafer stage of the second lithography tool 302Bat 406. The detector structure 200 may measure dose and/or intensity ofthe second lithography tool 302B. The computer 304 or a user may adjustthe second lithography tool's calibration based on the measured doseand/or intensity. The actions described above at 400-404 may be repeatedfor the second lithography tool 302B and other lithography tools.

Thus, the detector structure 200 and computer 304 may be used tocalibrate two or more lithography tools. The detector structure 200 andcomputer 304 may be used to match intensity and dose of two or morelithography tools.

FIG. 5 illustrates an alternative embodiment of a dose transfer standarddetector structure 500. The detector structure 500 may have detectors,amplifiers and alignment marks which are substantially similar to thedetectors 206, amplifiers 202 and alignment marks 205 of the detectorstructure 200 in FIG. 2. The detector structure 500 may be inserted in alithography tool 502. The lithography tool 502 may have sensors orprobes 504 which contact the detector structure 500 to establish anelectrical connection and read intensity and/or dose data from thedetector structure 500.

A number of embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made without departing fromthe spirit and scope of the application. For example, the structures andtechniques described above may be used to measure and calibrateintensity and does for other lithography tools besides EUV lithographytools. Accordingly, other embodiments are within the scope of thefollowing claims.

1. An apparatus comprising: a wafer adapted to fit on a wafer stage of alithography tool; a radiation detector attached to a surface of thewafer, the radiation detector to produce a signal corresponding to anamount of radiation detected from the lithography tool; and a processorcoupled to the radiation detector, the processor to process the signalfrom the radiation detector.
 2. The apparatus of claim 1, furthercomprising a transmitter coupled to the processor, the transmitter towirelessly transmit a signal from the processor.
 3. The apparatus ofclaim 1, wherein the detector is adapted to detect a dose of radiationfrom the lithography tool.
 4. The apparatus of claim 1, wherein thedetector is adapted to detect an intensity of radiation from thelithography tool.
 5. The apparatus of claim 1, wherein the detectorcomprises an array of detectors.
 6. The apparatus of claim 1, furthercomprising alignment marks adapted to align the wafer on the wafer stageof the lithography tool.
 7. The apparatus of claim 1, further comprisingan amplifier coupled to the radiation detector and the processor, theamplifier to amplify the signal from the radiation detector and transferthe amplified signal to the processor.
 8. The apparatus of claim 1,further comprising a power source coupled to the processor.
 9. A systemcomprising: a processor; and a radiation detector adapted to communicatewith the processor, the radiation detector to fit on a wafer stage of alithography tool, the radiation detector to detect an amount ofradiation from the lithography tool and transmit data corresponding tothe amount of radiation to the processor, the processor to compare thedata corresponding to the amount of radiation to a setting of thelithography tool.
 10. The system of claim 9, wherein the processor isadapted to use the data corresponding to the amount of radiation tocalibrate the lithography tool.
 11. The system of claim 9, wherein theradiation detector is adapted to wirelessly transmit data to theprocessor.
 12. An apparatus comprising: a wafer sized to fit on a waferstage of a lithography tool; a radiation detector attached to a surfaceof the wafer, the radiation detector to produce a signal correspondingto an amount of radiation from the lithography tool; a processor coupledto the radiation detector, the processor to process the signal from theradiation detector; and a memory coupled to the processor, the memory tostore data from the processor, the data corresponding to an amount ofradiation from the lithography tool.
 13. The apparatus of claim 12,further comprising an output connector adapted to output data from thememory.
 14. The apparatus of claim 12, further comprising a transmittercoupled to the memory, the transmitter to wirelessly transmit data fromthe memory.
 15. An apparatus comprising: a wafer sized to fit on a waferstage of a lithography tool; a radiation detector fabricated on asurface of the wafer, the radiation detector to produce a signalcorresponding to an amount of radiation from the lithography tool; aprocessor attached to the surface of the wafer, the processor coupled tothe radiation detector, the processor to process the signal from theradiation detector and output the data to the lithography tool.
 16. Theapparatus of claim 15, further comprising a memory to store data fromthe processor.
 17. A method comprising: loading a wafer-shaped detectoron a wafer stage of a first lithography tool; detecting an amount ofradiation from the first lithography tool; and transmitting a firstsignal indicative of the amount of radiation detected by the detector.18. The method of claim 17, wherein said transmitting compriseswirelessly transmitting the first signal indicative of the amount ofradiation detected by the detector.
 19. The method of claim 17, furthercomprising aligning the wafer-shaped detector on the wafer stage. 20.The method of claim 17, further comprising converting the first signalcorresponding to the amount of radiation detected by the detector to asecond signal adapted to be wirelessly transmitted.
 21. The method ofclaim 17, wherein said detecting the amount of radiation comprisesmeasuring a dose of radiation.
 22. The method of claim 17, wherein saiddetecting the amount of radiation comprises measuring an intensity ofradiation.
 23. The method of claim 17, further comprising amplifying thefirst signal from the detector.
 24. The method of claim 17, furthercomprising removing the wafer-shaped detector from the wafer stage. 25.The method of claim 17, further comprising comparing the amount ofradiation detected by the detector to a pre-determined reference value.26. The method of claim 25, further comprising adjusting a setting ofthe lithography tool if the amount of radiation detected by the detectordoes not substantially match the pre-determined reference value.
 27. Themethod of claim 26, further comprising repeating said detecting anamount of radiation from the first lithography tool on the detector, andtransmitting a second signal indicative of the amount of radiation fromthe first lithography tool detected by the detector.
 28. The method ofclaim 17, further comprising: loading the wafer-shaped detector on awafer stage in a second lithography tool; detecting an amount ofradiation from the second lithography tool; and transmitting a secondsignal indicative of the amount of radiation detected by the detector.29. The method of claim 28, further comprising comparing the amount ofradiation detected by the detector in the first lithography tool to theamount of radiation detected by the detector in the second lithographytool.